Balloon dilatation catheters are used for a wide variety of medical procedures, typically to enlarge a body lumen that has become obstructed. For example, balloon dilatation catheters commonly are used in angioplasty procedures to enlarge the lumen of a blood vessel constricted or stenosed by arteriosclerosis. Recent years have seen significant advances in percutaneous transluminal coronary angioplasty in which a dilatation catheter having a relatively inelastic polymeric balloon on its distal end is advanced percutaneously into the patient's arterial system and into the coronary artery to be treated. The balloon is inserted into the stenosis and is inflated to effect the dilatation. Such catheters also are used to perform angioplasty procedures on peripheral arteries as well. U.S. Pat. No. 4,195,637 to Gruntzig discloses such angioplasty catheters. Balloon dilatation catheters also are used to dilate other body lumens, such as, for example, in the esophageal tract, blood vessels and the like.
Balloon dilatation catheters often are used in conjunction with another tubular guide member through which the dilatation catheter is inserted and guided to the desired location in the body lumen of the patient. For example, the aforementioned Gruntzig Patent illustrates the use of a guide catheter in connection with percutaneous transluminal coronary angioplasty. Dilatation balloons used to treat a patient's gastrointestinal tract often are inserted into the patient through an endoscope. Endoscopes vary in length, depending on their intended purpose. For example, a typical multi purpose gastrointestinal endoscope may be of the order of four and one-half to five feet long and may be of the order of one inch diameter. It is formed from a plurality of articulated sections so that it is flexible. Controls, such as pull wires, are provided at the proximal end of the endoscope to control the shape of the distal end to steer and directionally control the endoscope. The endoscope typically has multiple channels for various functions and usually includes optical fiber channels to illuminate and permit visual observation of the patient's gastrointestinal tract. One or more channels, often only a few millimeters in diameter, also are provided through which instruments may be inserted into the patient such as, for example, miniature biopsy forceps, snares, needles, brushes, balloon dilatation catheters and others. An illustrative procedure may involve dilatation of the esophagus in order to enlarge a constriction caused, for example, by a tumor, esophagitis or other condition. In the procedure, the endoscope is passed through the patient's throat and into the esophagus. The progress of the endoscope is monitored visually through the fiber optic and illumination system. When the obstructed portion of the esophagus is reached, a dilatation catheter having a balloon at its distal end is passed through the instrument channel, with the balloon deflated, so that the balloon exits the distal end of the endoscope and passes through the obstruction. Once the balloon is placed within the obstruction, it is inflated to dilate the obstructed portion of the esophagus. The balloon must be deflated to a low profile in order for it to be passed through the instrument channel. Typically, the balloon is deflated by applying negative pressure to the balloon through an inflation/deflation lumen that extends from the proximal end of the catheter to the interior of the balloon.
Among the difficulties with dilatation balloons is the configuration that is assumed by the balloon when it is deflated. Typically, the balloon forms a pair of opposed, radially extending flat wings when it collapses under the influence of negative pressure. In order to insert the balloon into the instrument channel (or guide catheter lumen), the physician typically will manually wrap the wings about the catheter shaft and will insert the balloon catheter into the channel or guide catheter lumen in that configuration. The reduced profile also facilitates insertion of the balloon end of the catheter through the constriction. After the balloon has been inflated to perform the dilatation, it typically is deflated and, when that is done, it tends to assume the two wing configuration. The wings typically extend diametrally a distance substantially larger than the diameter of the channel. If it is desired to leave the endoscope in place and withdraw the dilatation catheter through the channel, that may present problems if the wings fail to wrap about the catheter shaft as the balloon is drawn into the channel. The wings may become caught at the distal end of the channel or otherwise interfere with smooth withdrawal. Withdrawal of the catheter may be necessary when it is desired to change catheters during the procedure, for example, as when the physician decides that further dilatation with a larger diameter balloon is required.
The foregoing problem has not gone unrecognized. Attempts to deal with it are evidenced by patented devices which seek to provide a means to cause the balloon to be wrapped closely about the catheter shaft to form a reduced profile. See, for example, U.S. Pat. No. 4,292,974 to Fogarty. Although such devices may have had some limited success, there remains a need for a simple effective means to facilitate collapse of a dilatation balloon to a low profile.